I've had a reckoning with my caffeine metabolism recently. I fall asleep very easily, like head hits pillow and I'm zonked within a minute. But I often wake up at 3 or 4am and am unable to go back asleep.

What I've learned is that caffeine metabolism goes down with age and sleep gets lighter with age. Even if you can fall asleep easily, the residual caffeine in the middle of the night is enough to wake you out of light sleep. I made a tool to convince myself to cut back: http://jitterdone.com

This was my immediate thought. Very small amounts of daily coffee have caused me significant problems with fatigue etc... Takes 1-2 months to get back to feeling good. Strongly urge anyone who feels tired, lack of focus etc to stop all caffeine intake. As with any drug, you're just chasing the initial boost, and really only getting yourself back to baseline.